Average Coin Age estimates the mean age of coins in the current held-supply distribution. It is derived from HODL Waves by assigning each age band a midpoint in days and weighting those midpoints by band share, so it summarizes held-supply age in one number rather than showing the full age curve.
A rising series means the held-supply profile is aging and more supply is sitting in older cohorts. A falling series means the distribution is becoming younger as turnover resets supply into newer bands. It is most useful beside HODL Waves and spent-age metrics.
The key caveat is estimation. This is not an exact mean over per-coin ages in the full UTXO set, but a midpoint-based summary of age bands. Different band shifts can therefore produce similar averages, which is why the full HODL Waves chart still matters.
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